Apparatus and methods whereby tubular sheets of nonwoven, melt-blown continuous fibers are formed by directing attenuated molten polymer streams toward a rotating collection mandrel are well known in the art as evidenced by U.S. Pat. Nos. 3,905,756 to Bringman, 3,905,734 to Blair, 3,909,174 to Blair et al, 3,933,557 to Pall, 4,021,281 to 4,021,281 to Pall and 4,032,688 to Pall (the entire content of each patent being expressly incorporated hereinto by reference). In general, the apparatus and methods disclosed in the known prior art include a downstream winder assembly which rotates synchronously with the collection mandrel. Thus, the melt-blown fibers are collected on the circumferential surface of the rotating mandrel to form a nonwoven tubular sheet which is withdrawn from the mandrel at a substantially constant rate by the synchronously rotating winding assembly.
During manufacture of nonwoven sheets using a winding assembly which is synchronously rotated with a collection mandrel, it is very important that substantially constant tension be maintained on the sheet as it is being withdrawn from the collection mandrel. Otherwise, variations in sheet tension could result in thickness variations and/or other imperfections in the resulting melt-blown nonwoven sheet product.
Broadly, according to the present invention, substantially constant sheet tension is accomplished by virtue of a continual increase in the longitudinal distance (in relation to the machine direction) between the collection mandrel and the take-up roller. Most preferably, such increased longitudinal distance is achieved according to this invention by mounting the take-up roller for linear movements relative to the collection mandrel to accommodate the increasing diameter of the sheet material being wound convolutely on the take-up roller.
Further tension controls are exercised on the sheet material according to the present invention by means of a pneumatically operated pressure-regulating system. Generally, the pressure-regulating system of the present invention includes at least one rotatable press roller which is longitudinally fixed in position relative to the collection mandrel in contact with the sheet material being wound around the take-up roller. The take-up roller is pneumatically advanced toward the press roller by the pneumatic actuation of at least one air cylinder. Thus, as the diameter of the sheet material being wound around the take-up roller increases, the pneumatic ram of the air cylinder will cause the pneumatic pressure of the air cylinder to correspondingly increase. This increase in pneumatic pressure is sensed by a pneumatic pressure regulator which vents sufficiently to decrease the pneumatic pressure acting on the air cylinder to a predetermined set point pressure. In this manner, therefore, the pressure exerted on the sheet material between the positionally fixed (but rotatable) press roller and the longitudinally movable take-up roller is maintained substantially constant during production of the nonwoven sheet material.
These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed disclosure of the preferred exemplary embodiments thereof.